HKDD exists primarily as a convenience for software developers whose programs were originally designed for Win95. Applications written for Windows NT and Windows 2000 (notably the Performance Monitor) don’t get data out of HKDD; instead, they use HKEY_PERFORMANCE_DATA. However, Win95 code that uses subkeys of HKDD will still work, since the NT family remaps HKDD data into the appropriate subkeys elsewhere in the Registry.